This project proposes to study the morphogenetic expression of determination in chick embryos. The complex morphogenesis of the mesoblast layer into metameric structures (somitomeres) provides a blueprint for the migration of cranial neural crest cells. The very early events that elicit and pattern somitomeres, as well as those secondary tissue interactions that result in the patterned emergence of cranial neural crest cells will be studied by light and electron microscopy, microsurgical intervention, in vitro culture of explants and tissue recombinants, analysis of quail-chick chimeras, and immunological and biochemical means. Specifically, this study includes 1) a clarification of the morphogenetic events that lead to the determination of somitomeres in the head and trunk, 2) an evaluation of the morphological relationship between somitomeric pattern in the head process and subsequent branchiomeric development, 3) an assessment of the role of extracellular matrix-cell interaction in the iniation and establishment of somitomeric pattern and in the establishment and maintenance of the otic placode, 4) an evaluation of the role of the otic epithelium and somitomeric pattern on otic neural crest cell migration, 5) a comparison of somitomeric pattern development in the cranial region of different groups of vertebrates, and 6) quantitation and mapping of the cell surface-associated matrix molecules in patterned craniofacial structures. What may be learned from this research will be relevent to our basic understanding of normal development in general, and craniofacial anomalies in particular.